Previous work in our laboratory has shown that "Immune" RNA extracted from lymphoid or organs of immunized animals will mediate cellular immunity to transplantation antigens and to tumor specific transplantation antigens. Direct systemic administration of "Immune" RNA or spleen cells preincubated with "Immune" RNA caused resistance to tumor isografts in vivo and specific lysis of tumor target cells in vitro. Xenogeneic, allogeneic and syngeneic sources of "Immune" RNA have been used. We propose to study the kinetics of "Immune" RNA synthesis by lymphoid cells, to identify the population of lymphoid cells that synthesizes "Immune" RNA, to identify and partially characterize the active moiety or moieties in our RNA preparations, and to identify the effector cell population that is converted to specific immunoreactive status by "Immune" RNA. Discontinuous density gradient techniques for separating lymphoid cells and several preparative techniques for isolating RNA fractions will be used. These studies will contribute to our understanding of the mechanism of action of "Immune" RNA. Such knowledge may enable us to increase the magnitude of antitumor immune responses mediated by RNA.